This invention relates to a method and apparatus for selecting an access technology in a multi-mode terminal. In particular, this invention relates to a method and apparatus for selecting an access technology that requires a minimal amount of power in the multi-mode terminal to achieve a maximum transmission duration capability.
Several access technologies exist today to facilitate the transmission of voice and data information over mobile radio communications systems. Examples of these technologies include: wideband code division multiple access (W-CDMA), enhanced data rates for global evolution (EDGE) classic and compact, global system for mobile communication, advanced mobile phone service (AMPS), and others. These technologies operate over different frequency bands and utilize various signaling approaches in order to transmit information over a communication network. As a result of these variations, several different access technologies may be used within a single coverage area, such as a cell, microcell, or picocell. Each of the access technologies generally utilizes a respective radiating power level. This, in turn, requires a battery of a terminal operating within the communication network to be capable of supplying a current that is proportional to the radiating power level of the technology used to access the network.
As the number of access technologies has increased, it has become desirable to design terminals to have the capability of transmitting information using more than one access technology. General aspects of such terminals are known in the art, as described by U.S. Pat. No. 5, 845,215 to Henry et al., entitled xe2x80x9cOperating Mobile Stations of Wireless Communication Systems in Multiple Modes by External Controlxe2x80x9d, the disclosure of which is expressly incorporated herein by reference.
These so-called xe2x80x9cmulti-modexe2x80x9d terminals allow users to choose the technology used to access the communication network depending on a number of factors. Typically, this choice involves balancing the cost of network access against the amount of services that may be available within the network for a given access technology. For example, the W-CDMA and EDGE access technologies may offer services such as voice mail or Internet access capability that are in addition to the services offered by the GSM or AMPS technologies operating within the same coverage area of the network. However, these added services may require a user to incur additional charges to access the network in comparison to access technologies that do not offer these services.
In addition to allowing users to choose a particular access technology, it is desirable to have multi-mode terminals that are capable of automatically selecting an access technology based upon a set of input parameters in order to achieve a desired functionality. One such terminal is described in U.S. Pat. No. 5,999,829 to Chun et al. (xe2x80x9cChunxe2x80x9d). Chun""s terminal is capable of automatically selecting between CDMA and frequency division multiple access (FDMA) access modes depending on a received electric field signal strength. As described by Chun, if the received signal strength for the CDMA mode exceeds a predetermined threshold level, the terminal accesses the communications network via the CDMA access technology. Otherwise, FDMA signaling techniques are used to access the network. Like many other conventional systems, Chun""s terminal is biased towards selecting the CDMA signaling mode over the FDMA mode because of the added services available to the users of terminals that utilize the CDMA technology.
A disadvantage associated with these systems, however, is that such biasing in favor of a particular access technology (such as CDMA in the system of Chun) precludes the automatic selection of an access technology for a given terminal type that is optimal for some other function, such as maximizing the transmission duration capability of the terminal. Maximizing the transmission duration capability is often of particular importance, e.g., when sending an emergency voice message or transferring critically needed data over the communication network at a time when the energy stored in a terminal""s battery is low.
As discussed above, each of the different access technologies utilizes a respective radiated power level, requiring a corresponding respective battery supply current to power the device. Access technologies utilizing higher radiated power levels require higher supply currents, while those technologies utilizing lower radiated power levels require lower supply currents. In addition, these radiated power levels may be reduced if the received electric field strength is strong enough to sustain a communication link with the network for a given type of information transfer. Also, the supply current requirements needed to sustain the different radiated power levels can vary from terminal to terminal. Moreover, certain access technologies may be capable of supporting only a particular type of information transfer (e.g., AMPS is not capable of receiving data from the Internet). If these factors could be evaluated by a terminal device, such that the access technology requiring the minimum battery supply current to sustain the desired network connection could be determined, then the transmission duration for that network connection could be maximized.
Thus, there is a need for determining, in a multi-mode terminal device, an optimal network access technology so as to maximize the transmission duration capability of the device.
It is therefore an object of the invention to select an access technology that requires a minimal amount of power in a multi-mode terminal to achieve a maximum transmission duration capability. It is yet another object of the invention that the selected access technology be capable of transmitting the type of information being exchanged before the selecting has occurred.
According to the invention, these and other objects are met by a method and apparatus for selecting an access technology in a multi-mode terminal. Information is exchanged between a multi-mode terminal and a base station in a communication network using a first access technology, the multi-mode terminal being capable of exchanging information with the base station using a plurality of access technologies. The type of information exchanged is identified, and at least a second access technology is determined, different from the first access technology, that is capable of exchanging information of the identified information type. The first and the at least second access technologies form a plurality of compatible access technologies. A determination is made as to the minimum radiated power level necessary to exchange the information with the base station for each of the compatible access technologies. An optimal access technology, e.g., one requiring a lowest amount of battery energy among the compatible access technologies to maintain the minimum radiated power level, is selected to exchange the information between the multi-mode terminal and the base station.
According to an exemplary embodiment, determination of the minimum radiated power level is accomplished by measuring a received signal strength of signals received at the multi-mode terminal for each of the compatible access technologies. A minimum radiated power level is computed for each compatible access technology based on the corresponding received signal strength measurements.
According to another exemplary embodiment, selecting an optimal access technology is achieved by creating a table having table entries that include battery power levels required to operate the multi-mode terminal at a plurality of radiated power levels for each of the access technologies. A compatible access technology having the lowest battery power level for the determined minimum radiated power level is selected from the various table entries.